Growth cone guidance is critical for the establishment of appropriate connectivity among neurons and failures in this process can result in psychiatric and neurological disease. Several extracellular guidance cues and their receptors have been implicated in growth cone guidance. However, the intracellular mechanisms that mediate the response to these cues are not well understood. Activation of the Rac GTPase is thought to be a key step in the transduction of guidance signals. However, our understanding of the events downstream of Rac activation is limited. Recent work has implicated MIG-10/lamellipodin as an effector for Rac during the guidance response. Activation of Rac triggers binding to MIG-10/lamellipodin and asymmetric localization of MIG-10/lamellipodin in response to a guidance cue. The immediate goal of this application is to identify additional members of the MIG-10/lamellipodin signaling pathway. Identification of these proteins will provide preliminary data for a larger research application that will seek to determine how asymmetric localization of signaling complexes is established and how this asymmetric localization results in directional responses to guidance cues. PUBLIC HEALTH RELEVANCE: Mutations in genes that encode components of the Rac signaling pathway can cause mental retardation in humans. Furthermore, Rac inactivation has been implicated in the inhibitory signaling pathways that prevent neuronal regeneration. Therefore, an understanding of how Rac and MIG-10/lamellipodin function to control axon growth and guidance will be useful in efforts to treat mental retardation and neural injury.